1. Field of the Invention
This invention relates to an outboard motor mounted on the stern of a boat and having a propeller to propel the boat.
2. Description of the Related Art
Among of the outboard motors, hybrid outboard motors equipped with an internal combustion engine and an electric motor as propeller drive sources or propulsion unit have been developed.
In the hybrid outboard motors, for selectively transmitting either the output of an internal combustion engine or the output of an electric motor to a propeller, it is conceivable, as taught for example by Japanese Laid-Open Utility Model Application No. Sho 63(1988)-158,493 (e.g., FIG. 5), to connect one end of the output shaft of the electric motor to the output shaft of the internal combustion engine through a centrifugal clutch and connect the other end of the output shaft of the electric motor to the propeller. By this arrangement, during operation of the internal combustion engine, the engine output can be transmitted to the propeller through the centrifugal clutch and the output shaft of the electric motor, whereby the propeller can be driven either by the internal combustion engine alone or by both the internal combustion engine and the electric motor. On the other hand, when the internal combustion engine is not operating, the connection between the internal combustion engine and the electric motor is disengaged to enable driving of the propeller solely by the electric motor.
Although not related to hybrid outboard motors, Japanese Laid-Open Utility Model Application No. Sho 61(1986)-205,899 (FIGS. 1 and 2) and Japanese Utility Model Registration No. 2,549,003 (e.g., FIG. 1) teach methods for cooling an electric motor used to drive a propeller.
The second reference ('899) teaches a configuration in which a chamber accommodating an electric motor is equipped with a pipe communicating with the outside air and the air in the chamber accommodating the electric motor is ventilated through the pipe. The third reference ('003) teaches a configuration in which a radiator is provided in communication with a chamber accommodating an electric motor and the electric motor is cooled by circulating air between the chamber and the radiator.
Another electric outboard motor that uses an electric motor to drive the propeller has been proposed, for example, by Japanese Patent No. 2603841 (page 2, left column, line 33 to page 3, left column, line 16). In the proposed technique, the outboard motor has an attached bar handle such that the operator can rotate around its longitudinal axis to regulate the speed of the electric motor.
Aside from the above, in an outboard motor, the rotational output of an internal combustion engine or the like is ordinarily transmitted to a drive shaft oriented parallel to the vertical direction and the rotation of the drive shaft (rotation around its vertical axis) is transmitted to a propeller shaft after being converted to rotation around a horizontal axis by a bevel gear, as disclosed, for example, in U.S. Pat. No. 3,310,021.
Further, the conventional practice has been to mount an outboard motor on a boat by clamping a screw-type clamping device on the boat transom, as taught, for example, in Japanese Laid-Open Patent Application No. 2001-233,290 (e.g., FIG. 4).
When the burden on the operator is taken into consideration, the internal combustion engine should preferably be started using electric power. In the first prior art taught by '493, however, the electric motor cannot be used to start the internal combustion engine because the connection between the internal combustion engine and the electric motor is cut off when the internal combustion engine is not operating. The outboard motor therefore has to be provided with an additional electric motor for engine starting separately of the electric motor for driving the propeller. This is disadvantageous because it increases the size and cost of the outboard motor.